THE GENOME ORGANIZATION AND AFFINITIES OF AN AUSTRALIAN ISOLATE OF CARROT MOTTLE UMBRAVIRUS

The genomic sequence of an Australian isolate of carrot mottle umbravi rus (CMoV-A) was determined from cDNA generated from dsRNA. This provi des the first data on the genome organization and phylogeny of an umbr avirus. The 4201-nucleotide genome contains four major open reading fr ames (ORFs). Analysis suggests that ORF2 encodes an RNA-dependent RNA polymerase, that ORF4 encodes a movement protein, and that the virus h as no coat protein gene; The functions of ORFs 1 and 3 remain unknown. ORF2 is probably translated following ribosomal frameshifting. ORFs 3 and 4 are probably translated from a subgenomic mRNA. Sequence compar isons showed CMoV-A to be closely related to pea enation mosaic RNA2 ( PEMV-RNA2), but also to have affinities with the Bromoviridae. These f indings shed light on the relationships between the luteoviruses, PEMV , and the umbraviruses and on the relationships between the carmo-like viruses and the Bromoviridae. (C) 1996 Academic Press, Inc.